This application claims the benefit of British patent application Serial No. 0113633.2, filed on Jun. 5, 2001.
This invention relates to means for effecting fluid flow patterns in conduits, particularly but not exclusively conduits such as blood flow tubing and stents, and other tubing carrying fluids essential to life or industrial fluids.
WO00/38591 discloses conduits such as tubing and stents devised to induce helical flow in such a fashion as to eliminate or reduce turbulence and/or eliminate or reduce dead flow regions in the conduits. The conduit has internal helical grooving or ridging or other measures which induce such helical flow, taking into account the conduit dimensions and the viscosity and velocity of fluid.
External structures have been used to provide reinforcement of conduits (see for example U.S. Pat. Nos. 3,479,670 and 4,130,904), which may serve to protect the conduits from kinking or maintain conduits in an open positions but do not directly influence internal geometry of the conduit lumen. For example, in U.S. Pat. No. 3,479,670 the tube lumen remains smooth despite the presence of reinforcing polypropylene monofilaments wrapped around the tube.
In accordance with a first aspect of the present invention there is provided a conduit, adapted for flow of a fluid having characteristics and velocity and having a given diameter, by apparatus that imposes, maintains or reinforces a flow guiding formation internally of the conduit, the apparatus comprising a helical structure to cause helical, rotational flow eliminating or reducing turbulence and/or eliminating or reducing dead flow regions in the flow, when used for such a fluid flow.
In accordance with a second aspect of the invention, there is provided apparatus for forming a helical flow formation in a conduit, the apparatus comprising a helical structure, and being adapted to be engaged with a conduit for carrying a fluid, in use, such that the helical structure forms the helical flow formation inside the conduit, the angle of the helical flow formation being determined from the internal dimensions of the conduit, the fluid mass flow of the conduit, the pressure drop along the conduit and the turbulent kinetic energy within the conduit.
In accordance with a third aspect of the present invention, there is provided a method of determining the helix angle of a helical flow formation within a conduit, the method comprising specifying the internal dimensions of the conduit and an intended fluid mass flow through the conduit, and determining the helix angle from the pressure drop and the turbulent kinetic energy for a conduit having the specified internal dimensions and intended fluid mass flow.
Typically, the pressure drop and the turbulent kinetic energy are non-dimensionalized before the helix angle is determined.
Preferably, the helix angle is determined as the helix angle at which the non-dimensionalized pressure drop and the non-dimensionalised turbulent kinetic energy are substantially equal.
The helical flow formation may have a helix angle of between 5xc2x0 and 50xc2x0. For example, the helical flow formation may have a helix angle of about 8xc2x0, particularly but not exclusively in relation to arterial flow in leg arterial grafts.
Typically, the fluid to be carried by the conduit comprises a liquid. The fluid may be a solely a liquid, a liquid mixed with a particulate solid, or a liquified solid. For example, where the conduit is blood vessel, the liquid is blood.
Preferably, the side wall of the conduit is deformable and the apparatus is engaged with the external side wall of the conduit such that the helical structure deforms the side wall of the conduit to form the helical flow formation on the interior of the conduit.
The helical flow formation may effect a rotational flow. The rotational flow may comprise a helical and/or spiral flow component.
The helical structure may comprise ridges which define a specific profile of the helical flow formation which effects the fluid flow pattern. Additionally or alternatively, the helical structure may comprise grooves which define a specific profile of the helical flow formation which effects the fluid flow pattern.
The helical flow formation may be orientated with a Z twist. A Z-twist orientation (also referred to as a right hand helix) creates clock-wise flow-inducing in the forward flow direction. Alternatively, the helical flow formation may be orientated with an S twist (also referred to as a left hand helix).
The apparatus may comprise symmetrical protrusions and/or asymmetrical protrusions, the asymmetrical protrusions having a gradually sloping leading edge and a steep sloping rear edge.
The apparatus may comprise single-start or multistart grooving and/or ridging.
The apparatus may comprise a frame. The frame may be formed by circular, rectangular, ovoid and/or differently parts. The frame may comprise parts having at least two different diameters.
The apparatus may comprise metals such as stainless steel. Alternatively or additionally, the structure may comprise synthetic or other thermoplastic or plastifiable material, being plastified and reset in twisted condition. Suitable materials include polytetrafluoroethylene (PTFE, also known as xe2x80x9cTeflonxe2x80x9d), polypropylene, nylon or other synthetic material. Stainless steel or other metallic structures maybe coated with synthetic or other thermoplastic or plastifiable material.
The apparatus may have a twisted appearance with an oval, rectangular or other non-circular cross-section. The structure may be coiled along its longitudinal axis and have a circular cross-section.
The apparatus may comprise patterned or solid material. The structure may be fixed or collapsable.
The helical flow formation may effect helical and/or spiral flow in such a fashion as to eliminate or reduce turbulence and/or eliminate or reduce dead flow regions in the conduit. Optimal helical angle to achieve such flow will depend on such factors as diameter of the conduit, longitudinal and rotational velocity of the fluid, and the viscosity and other characteristics of the fluid.
The apparatus may be branched.
The conduit may comprise tubing. For example, the conduit may comprise artificial or natural blood flow tubing, such as a graft or blood vessel, respectively. The tubing may be used in blood treatment or delivery equipment, for example a heat-lung machine, dialysis equipment or a giving set. The tubing may also be used in industrial equipment, for example hoses, pipes or fire hoses.
Alternatively, the conduit may comprise a stent. Stents, for example made of mesh, expanded sheet or tube or wire spring type, are inserted into blood vessels to provide mechanical support and prevent collapse of the blood vessel. A structure according to the present invention could be placed inside or outside the blood vessel to impose, maintain and/or reinforce a flow guiding formation through the blood vessel.
The invention may also be utilised for stent grafts, ie. a combination of stent and graft.
Also provided according to the present invention is a method for imposing, maintaining and/or reinforcing a helical flow formation which effects a desired flow configuration in a conduit, comprising fitting a support structure around the conduit wherein the structure imposes, maintains and/or reinforces the flow guiding formation.
Flow configuration through a conduit may, in general, be measured using such techniques MRI (magnetic resonance imaging) and/or Dxc3x6ppler ultrasound, and the flow guiding formation may be modified accordingly until a desired flow configuration is achieved. Initial design of flow configuration may be by mathematical modelling or by trial and error, with modification as described above.